CD-R is a digital optical disc storage format. A CD-R disc is a disc that can be written once. CD-R disks are readable by most plain CD readers, i. e. CD readers manufactured prior to the introduction of CD-R and this is an advantage over CD-RW, which can be re-written but cannot be played on many plain CD readers. The CD-R, originally named CD Write-Once, specification was first published in 1988 by Philips, the Orange Book consists of several parts, furnishing details of the CD-WO, CD-MO, and CD-RW. The latest editions have abandoned the use of the term CD-WO in favor of CD-R, written CD-Rs and CD-RWs are, in the aspect of low-level encoding and data format, fully compatible with the audio CD and data CD standards. This means they use Eight-to-Fourteen Modulation, CIRC error correction, and, for CD-ROM, properly written CD-R discs on blanks of less than 80 minutes length are fully compatible with the audio CD and CD-ROM standards in all details including physical specifications. 80 minute CD-R discs marginally violate the Red Book physical format specifications, CD-RW discs have lower reflectivity than CD-R or pressed CDs and for this reason cannot meet the Red Book standard. Some hardware compatible with Red Book CDs may have difficulty reading CD-Rs and, because of their lower reflectivity, especially CD-RWs. To the extent that CD hardware can read extended-length discs or CD-RW discs, it is because that hardware has capability beyond the minimum required by the Red Book and Yellow Book standards. The dye materials developed by Taiyo Yuden made it possible for CD-R discs to be compatible with Audio CD, a standard CD-R is a 1.2 mm thick disc made of polycarbonate about 120 mm or 80 mm diameter. The 120 mm disc has a capacity of 74 minutes of audio or 650 Megabytes of data. Despite the foregoing, most CD-Rs on the market have an 80-minute capacity, there are also 90 minute/790 MiB and 99 minute/870 MiB discs, although they are less common. Also, due to the limitations of the structures in the ATIP,90 and 99 minute blanks will identify as 80 minute ones. Therefore, in order to use the capacity, these discs have to be burned using overburn options in the CD recording software. Nothing in the Red, Yellow or Orange Book standards prohibits disc reading/writing devices from having the capacity to read or write discs beyond the Compact Disc standards, the polycarbonate disc contains a spiral groove, called the pregroove, to guide the laser beam upon writing and reading information. The polycarbonate disc is coated on the side with a very thin layer of organic dye. Then, on top of the dye is coated a thin, reflecting layer of silver, finally, a protective coating of a photo-polymerizable lacquer is applied on top of the metal reflector and cured with UV-light. A blank CD-R is not empty, the pregroove has a wobble, maintaining a constant rate is essential to ensure proper size and spacing of the pits and lands burned into the dye layer
Photomicrograph of the groove in a CD-R disc
An example of a CD-R burned in 2000 showing dye degradation in 2008. Part of the data on it has been lost.